... tanker (milk tank trailer)3-60tons:All the heads are one time moulding . And all the ... 5-3mm / outer shell 2mm, one time molding heads.2 .Special welding process :TIG welding process, to ... time molding heads and injecting PUF or use fiber glass.And each compartment use double heads back-to- ... back which make sure every compartment heads smooth and no right ...